Method for cooling electrical components in a plastics processing machine

ABSTRACT

A cooling method that involves circulating a liquid coolant through the motor housings and mounting surfaces for electrical/electronic components, such as the electric motors and associated electronic drives, in electric plastic processing machines. Specifically, the motors are provided with a housing having an integral heat exchanger, such as stainless steel tubing cast into a cylindrical aluminum stator housing. The various electrical/electronic components are mounted to the surface of a plate type heat exchanger (chill plate) that is contained within the electrical cabinet for the primary electrical circuitry. In addition, the air within the electrical cabinet is continually circulated over the chill plate to provide a more uniform temperature distribution within the enclosure and minimize condensation on the surface of the plate. The heat generated by the motors and electronics is absorbed from the motor housings and chill plate by the circulating liquid and released through a heat exchanger.

This is a division of application Ser. No. 08/231,080, filed Apr. 22,1994, now U.S. Pat. No. 5,523,640.

FIELD OF THE INVENTION

The present invention relates to liquid cooling of electricalcomponents, and more particularly to a combined system to provide liquidcooling of the electrical motors and associated drives in a plasticsprocessing machine, such as an injection molding machine.

DESCRIPTION OF THE RELATED ART

It is well known that electric motors produce heat during theiroperation. Usually the amount of heat produced increases with theincreasing horsepower of the electric motor. This heat causes breakdownof the insulation of the wiring, reduces the efficiency of the motor,causes deterioration of non-metallic components, such as seals, and canproduce premature failure of metallic parts of the motor. In particular,the heat generated during application of high current to a ceramicmagnet DC motor can degrade the magnetic properties, resulting in areduction of torque available from the motor. As plastics processingmachines, such as injection molding machines, increasingly use electricmotors to power the drive systems of the machine, the problem of heatdissipation increases.

Attempted solutions to the problem of removing heat from electric motorshas been approached in a variety of ways. For example, fins have beenused on motor housing to dissipate the heat, fans have been incorporatedinside electric motors for air cooling, air circulation patterns ofnumerous designs inside electric motors have been used, and externallymounted blowers have been used to maximize air cooling capability.However, these methods of air cooling are largely ineffective for motorsin plastics processing machines where the motors typically run at highcurrent but low rotational speed. The high current generates significantheat, but the low speed renders integral, rotor mounted fansineffective. The external blowers are not a satisfactory solution due tothe high audible noise and possibility of contamination associated withthis type of forced air circulation.

Since the thermal conductivity for a liquid coolant is much better thatcirculating air, a known alternative to air cooling of electric motorsis liquid cooling. Where liquid cooling of an electric motor has beenused, one approach is to provide the motor with a heat exchange jackethaving passageways for the circulation of the liquid through the jacket.Alternatively, a liquid-cooled motor can have a cooling liquidcirculated through the laminated core of the stator. In both of thesecooling methods there is an advantage over an air cooled motor in thatthe cooling median is capable of a high heat removing efficiency, andthus the fluid cools the motor at a high efficiency. In some cases, withthe higher efficiency of liquid cooling, it is possible to reduce thesize of an electric motor required for a particular application,resulting in a more economical machine construction.

It should be noted, however, that liquid cooling of motors has not beenused in plastics processing machines. Instead, prior art solutions formotor temperature control in machines of this type have involvedexternal forced air circulation and/or limiting functional capabilities.As proposed by U.S. Pat. No. 4,837,490, for example, when overheatconditions are detected, the injection molding cycle time is lengthenedto reduce the load on the motors. To make the motors more resistant tothe negative effects connected with high current and elevated operatingtemperatures, expensive rare earth magnets are often used as analternative to ceramic magnets, since they are less affected by suchconditions.

In addition to the previously stated problems associated with motors,the reliability of many electronic components is known to decreasesignificantly with increasing temperature. It is also known that theoperating characteristics for these electronic components varyappreciably over their range of operating temperatures so that theperformance often deteriorates significantly with increasingtemperature. It has also been found that less power is required tooperate a component when the component is maintained at a coolertemperature. At high temperatures, however, such devices require morepower to operate, to a point where they can be rendered virtuallyunusable; this can occur long before complete failure of the componentis reached. In fact, it has been generally found that the life span ofsome electronic components is directly related to the temperatures atwhich the component operates. In general, the life span of someelectronic components may be cut in half by increasing the operatingtemperature of the component by 10° C.

The primary device typically used to cool electrical/electroniccomponents, such as those found in drives for electrical motors, is aheatsink. A heatsink generally consists of a large conducting plate towhich the electronic components are attached in a heat conductingrelationship. Since a significant number of components are included inelectrical motor drive systems, forced air is typically circulated overthe heatsinks to enhance the cooling effect. However, in some cases, theforced air approach has been proven to be only marginally effective. Forexample, airborne contaminants may be drawn into the forced air system,causing problems related to filtering, corrosion of components, andsurface build-up that impedes heat transfer.

An effective alternative to forced air is to mount the components on anindependently cooled, plate type heat exchanger. Passageways of sometype are formed in the plate so that a cooling fluid can be circulatedthrough the plate, the plate in effect operating as a form of heat sink.Precise temperature control of the plate is very important to avoidcondensation of moisture from the ambient air. The use of plate typeheat exchangers in different applications has shown that it is desirableto have the ability to remove the electronic components easily from theplate, perhaps in a modular fashion.

In electrically driven plastics processing machines there may be as manyas three or more high horsepower electric motors and associatedelectronic drives which require cooling. Although liquid cooling systemshave been proposed for electronics and motors separately, there has notbeen a combined system with sufficient capacity to cool both the motorsand drives used in machines of this type. The advantages of a combinedliquid cooling system in plastics processing machines have not beenachieved in prior art systems where heat generated by the motors iscontrolled by simply limiting machine capabilities.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to overcome theshortcomings of the prior art and provide a cooling system specificallyadapted to plastic processing machines which will extend the life ofelectronic components and provide more efficient and consistent motoroperation.

The present invention accomplishes the stated objective by providing acooling system which circulates a liquid through the motor housing andmounting surfaces for electronic components. This system is particularlycost effective where there are multiple electric motors and associatedelectronic drives, as in electric plastic processing machines. Ifdesired, other machine elements or systems requiring cooling, such asthe feed throat of the injection unit, can also be included in thesystem.

For example, the present invention can be used in an electric injectionmolding machine to cool the motors that drive mechanisms for the clamp,injection, extruder and part ejection systems, as well as the associatedelectronic drives. Specifically, the motors are provided with a housinghaving an integral heat exchanger, such as stainless steel tubing castinto a cylindrical aluminum housing. This allows for rapid dissipationof the heat produced by high current loading, effectively maintaining asafe, uniform operating temperature for the motor. Since the operatingtemperature is maintained at a desired level, the motor's permanentmagnets are less susceptible to weakening or demagnetization,facilitating use of economical ceramic magnets.

The electronic components are mounted to the surface of a plate typeheat exchanger that is contained within a compartment for the primaryelectrical circuitry. In addition, the air within the electricalenclosure is continually circulated to enhance the heat exchangecapabilities of the plate, providing a more uniform temperaturedistribution within the enclosure and minimizing the likelihood ofcondensation on the surface of the plate. The heat generated by themotors and electronics is absorbed from the motor housings and plate bya circulating liquid and released to a heatsink. In one embodiment,certain electronic resistors, such as those used for dynamic braking,are cast into the plate-type heat exchanger so that the heat transferfrom these components is optimized and space is saved by making this anintegral construction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view of an injection molding machineequipped with a cooling system of the present invention.

FIG. 2 is a schematic diagram of the cooling system used in conjunctionwith the injection molding machine of FIG. 1.

FIG. 3 is a front elevational view of a plate-type heat exchanger (chillplate) with integral electrical components according to the presentinvention.

FIG. 4 is an enlarged end view of the chill plate shown in FIG. 3.

FIG. 5 is a cross-sectional view of the chill plate taken along line5--5 as seen in FIG. 4.

FIG. 6 is a cross-sectional view of the chill plate taken along line6--6 as seen in FIG. 4.

FIG. 7 is an assembly drawing for an electrical component mountingsystem incorporating the chill plate of FIG. 3.

FIG. 8 is an end view of the assembly shown in FIG. 7 as it ispositioned in the injection molding machine.

FIG. 9 is an end view of a motor housing with an integral heatexchanger.

FIG. 10 is a front elevational view of the motor housing shown in FIG.9.

FIG. 11 is a front elevational view of an alternate configuration forthe motor housing shown in FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Although the present invention is applicable to various plasticprocessing machines, the following description is presented inconnection with an injection molding machine having anelectro-mechanical drive system. Accordingly, a brief description ofthis type of machine is useful in understanding the present invention.

FIG. 1 illustrates an injection molding machine to which the coolingsystem of the present invention is applied. The machine is comprised ofa clamp unit 100 and an injection unit 102, each mounted on a base 105.

The clamp unit 100 is comprised of a stationary platen 110 and a dieheight platen 108 which are connected by four tie bars at the platencorners. Two tie bars 112 and 114 are shown. The tie bars operate asguides for a movable platen 116. Mold halves 118 and 120 are affixed tothe platens 116 and 110, respectively; and when the clamp is in theclosed position shown, a mold cavity 122 is formed between the moldhalves. A gate opening 123 passes through mold half 120 and stationaryplaten 110 to permit the injection of a plastic melt into the moldcavity 122. The moving platen 116 is operated by a clamp motor 124mounted on the stationary platen 108. The motor 124 is connected to aball screw 126 by a drive belt 127. A gear drive or other mechanicalcoupling may also be used. The ball screw nut 128 is mounted in a togglemechanism 130 which provides a mechanical advantage for the motor 124 inoperating the clamp unit 100.

The injection unit 102 includes an extruder mechanism comprised of atubular barrel 140 with an extruder screw 142 rotationally andtranslationally mounted therein. The screw is journalled in a stationarymember 144, and one end of the screw 142 is rotatably secured in amovable member 146. Rotational motion of the screw 142 is provided by anextruder motor 148 mechanically connected to the screw by a drive belt150; rotation may also be implemented by any other suitable mechanicaldevice. The movable member 146 rides on a pair of parallel bar guides,one of which is shown at 152, connected between the stationary members144 and 154. An injection motor 156 mounted on the member 154 isconnected to a ball screw 158 by a drive belt 160. The ball screw nut162 is mounted in the movable member 146; and therefore, the motor 156is operative to provide linear motion to the member 146 and the extruderscrew 142 toward or away from stationary platen 110.

An ejector unit 170 is integrated with the mold and is operative toeject the finished molded part as the mold opens. The ejector unit 170is coupled to an ejector motor 103. The machine control (not shown)activates the motor 103 at the appropriate time in the injection moldingcycle. The ejector unit 170 is preferably under servocontrol toaccommodate the various requirements and operations of different molds.

A die height unit 174 is typically integrated into the tie bars andplaten 108 shown in FIG. 1. The die height unit 174 provides anadjustment of the spacing of die height platen 108, including togglemechanism 130 and movable platen 116, relative to the stationary platen110 to accommodate different molds having different mold thicknesseswhen the molds are in the closed position. The die height unit 174 iscontrolled by a die height motor 176. The die height adjustment can bemanually controlled by the operator which results in the machine controlproducing forward or reverse command signals to the motor 176.

The injection sled 180 generally rides on tracks (not shown) on the base105 and supports the entire injection unit 102, thereby permitting theinjection unit 102 to be moved toward or away from the stationary platen110. The injection sled is mechanically coupled to a sled motor 182.Again, the operation of this unit can be manually controlled by theoperator which results in the machine control providing forward orreverse command signals to the motor 182. It should be noted that thevarious motors noted above could be AC induction, brushed AC or DC,brushless (permanent magnet) AC or DC, or any other type, as might bebest suited for the particular application. In fact, it is intended thatthe cooling system of the present invention accommodate any combinationof motor types, even linear motors, in order to optimize machineperformance.

The specific elements associated with the liquid cooling system of thepresent invention are identified in FIGS. 1 & 2. The cooling system is a"contained" system to minimize potential for contamination of thecoolant, having closed loop circulation of a suitable liquid coolant,such as a water/glycol mixture. Liquid not actively circulating throughthe conduits of the cooling circuit is stored in a reservoir 12.

Circulation of the fluid is initiated by a motor/pump 14 mounted on thereservoir. From the pump 14 the coolant flows to a flow divider manifold20. The manifold 20 is provided with output ports, five in theillustrated embodiment, to facilitate connection to suitable conduitsand distribution of the coolant to the injection motor 156, the extrudermotor 148, the clamp motor 124, the ejector motor 103 and a chill plate22. If desired, other machine elements or systems requiring cooling,such as the feed throat of the injection unit (not shown), can also beincluded in the cooling circuit. As illustrated in FIG. 2 the flowdivider 20 allows parallel supply circuits for the motors and chillplate, so that each is cooled independently.

From the motors and chill plate, the coolant flows through suitableconduits to a heat exchanger 16. The heat exchanger 16 is a conventionalliquid/liquid type unit, connected to a source 21 of tap or centralchiller water that provides the heat sink for the system. Preferably, awater saver valve 18 is provided in the water flow path to providetemperature control for the coolant, as will be more fully describedlater.

Referring to FIGS. 3-8, the chill plate 22 serves as a mounting surfacefor many of the electrical/electronic components required for operationof the injection molding machine, especially the high heat componentsassociated with the electronic drives for the motors. Generally, aseparate drive is provided for each motor, as well as a power supply 42for the separate drives. Preferably, the drives 44,46,48,50 and powersupply 42 are modular units to simplify mounting and service; FIGS. 7and 8 show the relative location of the power supply 42, extruder motordrive 44, injection motor drive 46, clamp motor drive 48, and eject/dieheight motor drive 50. As also seen in FIG. 3, the chill plate 22 isspecially adapted to provide a direct mounting surface for the heatproducing components of the drive systems; mounting holes 52 areprovided to facilitate attachment of the modular power supply 42 anddrives 44,46,48 and 50. The various electrical/electronic components areattached as convenient to facilitate heat exchange, keeping thetemperature of these components within the desired operating range tomaximize their service life.

The chill plate 22 is preferably a casting made of aluminum, including astainless steel tube 30 formed to provide a serpentine flow path throughthe plate 22 and cast into the plate 22, thereby optimizing its heatexchange capacity and minimizing corrosion potential. FIGS. 4 and 5 showthe relative position of the tube 30 in the plate and the preferredconfiguration, including inlet 28 and outlet 32.

Also cast into the plate 22 are dynamic braking resistors 34 and shuntloading resistor 36. The dynamic braking resistors 34 are used todissipate the electrical energy produced during stopping or rapidslow-down situations, when the motors may function momentarily asgenerators. The shunt resistor 36 is necessary for removing excessenergy from the DC bus (when DC motors are used). Since these resistorscan produce significant heat, casting them directly into the chill plateprovides effective heat transfer and confines them so the environmentwithin the electrical cabinet 56 is not overly affected by radiatedheat, while also providing a compact system which saves space within thecabinet.

The cooling of the various motors is preferably accomplished byproviding for coolant flow through the motors stator housing 38 as shownin FIGS. 9-11. The housing 38 is basically a cast aluminum cylindercontaining a stainless steel tube 40 formed in a helix and terminatingin an inlet 62 and outlet 64. Where high horsepower is required, themotors often have very long stator housings. In such cases, two or morepieces of tubing 40 can be used, as seen in FIG. 11, to provide bettertemperature control over the length of the housing 38. Other types offlow passages, such as cast or extruded channels could also providemeans for coolant circulation in the motor housing.

After coolant exits the chill plate 22 and motors 103, 124, 148 and 156,it is conveyed back to the reservoir 12. The coolant returning to thereservoir 12 is now at an elevated temperature and is passed throughheat exchanger 16 to lower the temperature to the desired operatinglevel. The flow of water through the heat exchanger 16 from source 21 isregulated by valve 18 in the outlet line 54 in order to removesufficient heat from the coolant so that it leaves the heat exchanger 16and returns for circulation at the desired temperature. This is simplyaccomplished by monitoring the temperature of the coolant where it exitsthe heat exchanger 16 and using a control algorithm to regulate thevalve 18, keeping the coolant within the desired temperature range. Thespecific temperature of the coolant is not critical, although it ispreferably as low as practical while still remaining above the dew pointto minimize condensation. It has been found, for example, that thepresent cooling system circulating coolant at a flow rate of about sixgallons per minute can maintain a suitable operating temperatureeffectively, within a range of about ±2° F.

In addition to the direct heat sink function described above, the chillplate 22 provides a means to provide temperature conditioned air withinthe electrical cabinet 56, allowing it to be closed to outside air. Thesheet metal support 24 for the chill plate 22 forms a plenum 25 behindthe chill plate 22. A blower 26 is mounted at the end of the plenum 25to provide a forced air flow through plenum 25. The location of theblower 26 is adjacent the inlet 28 of the chill plate 22. Since this isthe coldest part of the chill plate, any condensation of moisture in theair will occur on this part of the plate, where it can be directed awayfrom the electronic components and drained from the electrical cabinet56, if desired.

Referring again to FIGS. 1 and 2, a cycle of operation will briefly bedescribed starting with the clamp unit 100 in the illustrated closedposition. Also as illustrated, solid thermoplastic, thermoset or othermaterial from the hopper 166 will have been plasticized by the screw 142to form a quantity of liquid phase plastic melt or a "shot" in front ofthe screw. Plastication time is optimized by providing external heat tothe barrel 140, typically by a plurality of circumferentially mountedheater bands 141. To initiate an injection cycle, the machine controlprovides a velocity command to the motor 156 in order to move linearlymember 146 and screw 142 towards the platen 110. As the screw 142 moveslinearly in the barrel 140 toward the stationary platen 110, the plasticmelt is injected through the orifice 143 and gate opening 123 into themold cavity 122. When the screw 142 completes its linear motion, themachine control transfers to the pack cycle. During the injection cycleand subsequent pack and hold cycles, the extruder motor controller isprovided with a zero velocity signal to keep the extruder screw 142 fromrotating due to the linear forces exerted on the screw 142.

In the pack cycle, the object is to continue to push the material intothe mold to complete the mold filling process. At the end of apredetermined period of time, marking the end of the pack cycle, themachine control transfers to the hold cycle where pressure ismaintained. The pack and hold cycles require that the injection motor156 maintains a high torque (using high current) with little or norotation; this condition generates significant heat in both the motor156 and the components of the electronic drive 46. If motor temperaturerises significantly, the torque available at a given current decreases,and the current would have to be increased to maintain torque,generating additional heat. The circulation of coolant keeps the motorat a suitable temperature to maintain the desired torque at thecorresponding current, providing more efficient motor operation.

After a predetermined period marking the end of the hold cycle, themachine control transfers to a cooling cycle for a further period oftime while the molded part cools. During the cooling cycle, the machinecontrol initiates an extruder run cycle in which the extruder motor 148is activated to extrude a new shot of molten material to the front ofthe screw 142. At the same time, the injection motor 156 must beoperated to move the screw 142 away from the platen 110 whilemaintaining a predetermined pressure on the molten plastic material,i.e., a predetermined back-pressure on the extruder screw 142. Themachine control causes the extruder screw motor 148 to rotate the screwto plasticize more plastic material and carry it to the front of thescrew adjacent to the orifice 143. Simultaneously, the machine controlmay also cause the injection motor 156 to refrain to some degree fromrotating in order to generate a predetermined back-pressure on the screw142. As pressure builds up on the front of the screw, the drive controlwill have to supply more current to the motor 156 to maintain the zerovelocity, i.e., to keep the motor from rotating. As noted previously,the higher current tends to generate additional heat and the liquidcooling allows the motor 156 to maintain consistent operatingparameters. When the back pressure reaches the desired level, the motor156 is caused to rotate, moving the screw 142 away from the platen 110while also maintaining the predetermined back-pressure. Consequently, asthe screw 142 rotates to build a shot of molten plastic, the screw willbe moved away from the platen 110 with a controlled back-pressure untilthe full shot of plastic material is extruded.

When the screw 142 reaches a predetermined final position, the machinecontrol stops the operation of the extruder motor 148 and issues avelocity command to the drive control for the injection motor 156 tomove the screw further back, thereby relieving the pressure on themolten plastic material due to the back-pressure from the screw 142. Atthe end of the molded part cooling cycle, the control also provides avelocity command signal to the clamp motor 124 to shift the movableplaten 116 in the direction away from the stationary platen 110 to openthe mold. While the mold is opening, the control will provide commandsignals to the ejector unit 170 and ejector motor 103 to actuate themold part ejector mechanism (not shown) carried by the mold half 118.The finished part is ejected from the mold, and the ejector motor 103then returns the part ejector mechanism to its original position.

When a fully opened mold clamp position is detected, the control givescommand signals to begin to moving the platen 116 in the oppositedirection to again bring the mold halves together. The control will thengenerate velocity commands depending on the position of the platen 116to control acceleration and deceleration and bring the mold halves intocontrolled contact. For example, movable platen 116 may initially bemoved at a rapid rate toward stationary platen 110 to reduce overallcycle time until a predetermined position is reached. Thereafter, acommand representing a low velocity is provided until another positionis detected and contact of the mold halves is imminent. Under normalcircumstances, the mold halves will be brought together to the fullyclosed position. However, if there is interference between the moldhalves, a torque limit control will override the velocity control andreduce current to the motor to reduce motor velocity and motion toprotect the mold halves from damage caused by the interference.

Assuming the mold halves reach the fully closed position, the torquecommand value is increased, and a command is given to move the toggle toa lock-over position as shown in FIG. 1. The mold clamping force isdetermined and controlled by the final position of the toggle mechanism130. The machine is now ready to begin another full cycle. As with theinjection motor 156 during pack and hold, the clamp motor 124 has tomaintain torque with no rotation while the clamp is in the closeposition, generating significant heat. In fact, during the typicalinjection molding cycle there is a period of time when the clamp motor124 and injection motor 156 must simultaneously maintain torque with norotation; the liquid cooling system of the present invention has thecapacity to dissipate the heat generated under such circumstances.

One of the drawbacks to implementing a complete liquid cooling system ininjection molding machines is the extensive modifications required toadapt the components to liquid cooling (from air cooling); thesemodifications are complex and expensive. To reduce the expense andcomplexity of the system, the cooling circuit is preferably configuredto supply several motors and their drives which could be in parallel orseries. When the cooled components are configured in series, the coolantshould preferably circulate through one or more of the motors before itgoes to the chill plate 22. This configuration will raise thetemperature of the coolant slightly before it enters the chill plate,further minimizing the possibility of condensation forming in theelectrical cabinet.

As the size of the injection molding machine increases to a larger sizeto produce larger parts, e.g. 1500 tons or more of clamping force, twoor more motors may have to be ganged together in order to obtain thedesired mold clamping forces and injection/extrusion capabilities. Withthe present liquid cooling system, it is possible to use smaller motors,and, in some cases, only a single motor is required to operatesatisfactorily the clamp and injection unit for a wider range of machinesizes, including machines of over 700 tons of clamping force. Thecooling system maintains a consistent operating temperature regardlessof the operating parameters or surrounding environment; accordingly themotor can be sized for the normal operating conditions and does not haveto be "over-sized" to accommodate extreme temperature increases thatmight occur in certain installations.

While the invention has been illustrated in some detail according to thepreferred embodiment shown in the accompanying drawings, and while thepreferred embodiment has been described in some detail, there is nointention to thus limit the invention to such detail. On contrary, it isintended to cover all modifications, alterations, and equivalentsfalling within the spirit and scope of the appended claims.

What is claimed is:
 1. In an electrically powered and electricallycontrolled plastics processing machine having a plurality ofheat-producing electrical components, a method for cooling theelectrical components comprising the steps of:(a) circulating a liquidcoolant through a first circuit including a coolant inlet, a coolantoutlet, and a coolant passageway for circulating the liquid coolantthrough an electric motor, the coolant passageway being positionedinteriorly of the motor, thereby cooling the motor when it is inoperation; (b) circulating the liquid coolant through a second circuitincluding a plate member having a coolant inlet, a coolant outlet, andan interiorly positioned coolant passageway for circulating liquidcoolant through the plate member, wherein at least one electricalcomponent is mounted on a side of the plate member so that heat istransferred from the electrical component to the plate member, therebycooling the electrical component when a circuit including the electricalcomponent is energized; (c) controlling the flow of the liquid coolantso that it circulates through the first and second circuitsconcurrently; and (d) controlling the temperature of the liquid coolantby means including a heat exchanger connected with the coolant outletsof the first and second circuits so that the heat accumulated by theliquid coolant is transferred from the liquid coolant to a heat sink,after the liquid coolant passes through the motor and after the liquidcoolant passes through the plate member.
 2. A method according to claim1 further comprising the step of circulating air through a plenum formedon a cooled surface of the plate member to provide auxiliary cooling ofelectrical components contained within an enclosed electrical cabinet.3. A method according to claim 1 wherein the step of controlling theflow of the liquid coolant so that it circulates through the first andsecond circuits concurrently involves flow of the liquid coolant throughthe first and second circuits in parallel.
 4. A method according toclaim 1 wherein the step of controlling the flow of the liquid coolantso that it circulates through the first and second circuits concurrentlyinvolves flow of the liquid coolant through the first and secondcircuits in series.
 5. In an electrically powered and electricallycontrolled injection molding machine having at least one rotary electricmotor with an associated electronic drive, a method for cooling themotor and electronic drive comprising the steps of:(a) circulating aliquid coolant through a first circuit including a coolant inlet, acoolant outlet, and a coolant passageway for circulating the liquidcoolant through the rotary electric motor, the coolant passageway beingpositioned in the stator of the motor, thereby cooling the motor when itis in operation; (b) circulating the liquid coolant through a secondcircuit including a plate member having a coolant inlet, a coolantoutlet, and an interiorly positioned coolant passageway for circulatingliquid coolant through the plate member, wherein the electronic motordrive is mounted on a side of the plate member so that heat istransferred from the electronic drive to the plate member, therebycooling the electronic drive when it is energized; (c) controlling theflow the liquid coolant so that it circulates through the first andsecond circuits concurrently; and (d) controlling the temperature of theliquid coolant by means including a heat exchanger connected with thecoolant outlets of the first and second circuits so that the heataccumulated by the liquid coolant is transferred from the liquid coolantto a heat sink, after the liquid coolant passes through the motor andafter the liquid coolant passes through the plate member.
 6. A methodaccording to claim 5 further comprising the step of circulating airthrough a plenum formed on a cooled surface of the plate member toprovide auxiliary cooling of electrical components contained within anenclosed electrical cabinet and to reduce condensation on the platemember.